VALVE ACTUATING MECHANISM

Abstract

A mechanism for actuating an engine poppet valve includes two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the stem of the valve, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. In the invention, an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, and a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem. The latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.

Description

FIELD OF THE INVENTION

The invention relates to an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. Such valve actuating mechanisms are known per se and are described for example in U.S. Pat. No. 6,854,434, GB Pat. Appln. No. 0519876.7, and U.S. patent application Ser. No. 11/284,725.

BACKGROUND OF THE INVENTION

In addition to controlling engine valves to vary such parameters as phase, valve lift and event duration, cylinder deactivation is becoming increasingly common on large displacement gasoline engines, where significant fuel economy improvements can result from running an eight cylinder engine on four cylinders during light load operation. Deactivating one of a pair of intake valves on a diesel engine in order to control in-cylinder swirl levels is also an interesting concept for future research.

OBJECT OF THE INVENTION

The present invention therefore seeks to provide a system for controlling valve lift and duration which is additionally capable of deactivating one or more valves per cylinder.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams, characterised in that an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.

In the invention, two cams are used to actuate one or more valves via a summation system, and the valve lift characteristic can be changed by phasing one of the cam lobes relative to the other. Such systems can be arranged such that valve lift will only occur when both cam lobes are on lift and the valve will be closed if either of the cam profiles is on its base circle radius. It follows that there will be some clearance in the system during some portion of the camshaft cycle when both cams are close to their base circle radii, and it is this clearance that provides the opportunity for a valve deactivation system to operate.

Many valve deactivation and cam switching devices are known from the prior art that are designed to operate when the valve is closed (e.g. U.S. Pat. No. 6,196,175 US 2002/0014217 U.S. Pat. No. 6,135,074) but in conventional systems where there is little or no clearance when the valves are closed the switching of the valve deactivation system has to be carefully controlled in order to prevent the switching process from taking place when the valve begins to lift. This would be likely to cause overloading of the locking components and damage to the system. In order to avoid this, the switching of the systems applied to each cylinder of the engine is often controlled independently to make sure each cylinder switches fully whilst the valve is closed.

Unlike conventional valve train systems, the summation rocker system design requires the rocker system to move whilst the valve is closed and the system is not heavily loaded. This allows a number of different implementations of the present invention, in which use is made of this additional rocker motion to effect the switching of the rocker system to a deactivated mode of operation. This allows the timing of the switch to be controlled such that it will always occur whilst the valve is closed and also offers the opportunity for the deactivation system to be integrated into the design of the rocker system rather than being a totally separate system.

The different embodiments of the invention, which will be described below, offer the following advantages as compared with prior art systems, namely:

• • Additional valve train flexibility for advanced combustion strategies,
  • Valve deactivation occurs only whilst the valve is closed,
  • Valve deactivation and lift control systems can be integrated instead of being separate, and
  • The invention can be implemented in different ways to suit a wide variety of engine architectures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

FIGS. 1A and 1B are perspective views of two different types of known summation valve trains,

FIG. 2 is a graph showing the principle of operation of a summation valve train,

FIGS. 3A, 3B and 3C are a section, end view and perspective view, respectively, of a first embodiment of the invention in which a valve deactivation system is located in the position of a lash adjuster,

FIGS. 4A, 4B and 4C are similar views showing a modification of the valve deactivation system of FIG. 3,

FIGS. 5A and 5B show side and perspective views of another embodiment of the invention,

FIGS. 6A, 6B and 6C show isometric, side and exploded views of the deactivation system incorporated in the valve train of FIG. 5,

FIGS. 7A and 7B are isometric and side views, respectively, of a further embodiment of the invention using mechanical valve deactivation,

FIGS. 8A, 8B, 8C and 8D are respectively a section, an end view, a perspective view and an exploded view of a rocker in FIGS. 7A and 7B,

FIGS. 9A to 9F show end views and views from below of the rocker of FIGS. 7 and 8 in different positions,

FIGS. 10A and 10B show a side view and a perspective view, respectively, of an embodiment of the invention in which a single rocker is used to actuate two valves through a bridge piece,

FIGS. 11A to 11E are a side view, section, plan view from above, perspective view and an exploded view of one of the rockers in FIG. 10,

FIG. 12 shows the valves and bridge piece operated by the rocker in FIG. 11,

FIGS. 13A and 13B are assembled and exploded perspective views of a further embodiment of the invention,

FIGS. 14A to 14C are an exploded view from the opposite end and details of modifications of the embodiment shown in FIG. 13,

FIGS. 15A and 15B are assembled and exploded perspective views of a further embodiment of the invention,

FIGS. 16A, 16B and 16C are a perspective, plan and exploded view, respectively, of three-part rocker in FIGS. 15A and 15B,

FIGS. 17 A to C are different sections through the rocker of FIG. 16,

FIGS. 17D and 17E are sections similar to the sections of FIGS. 17A and 17B but showing the locking pins in a different position,

FIGS. 18A, 18B and 18C are a perspective view, a section and an exploded perspective view, respectively, of a rocker of a further embodiment of the invention,

FIGS. 19A and 19B show a valve train using the rocker of FIG. 18 in the deactivated and activated positions, respectively,

FIG. 19C shows a front view of the valve train of FIGS. 19A and 19B,

FIG. 20 is a perspective view of the valve train of FIG. 19,

FIG. 21A is a side view of a cam follower embodying the invention,

FIG. 21B is a section through the cam follower of FIG. 21A along the section line A-A in FIG. 21A,

FIGS. 21C to 21E are sections along the line B-B of FIG. 21B showing different states of the cam follower, and

FIGS. 22A, 22B, 22C and 22D are a side view, a partially cut away perspective view, a section and an exploded view, respectively, of a further cam follower embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings in this specification are derived from complete technical engineering drawings which show different practical implementations of the invention in more detail than is necessary for an understanding of the invention. The function of many of the components will be self-evident to the person skilled in the art and the description of the drawings will therefore be confined mainly to an explanation of the way in which valve deactivation is achieved.

Two different types of summation valve train have been considered for the application of valve deactivation systems as shown in FIGS. 1A and 1B, respectively. The valve train of FIG. 1A is for use in overhead valve engines where the camshaft is located in the cylinder block whilst the valve train of FIG. 1B is for engines with an overhead camshaft. In each of these valve trains, each valve 10 is acted upon by valve-opening rocker 12, the angular position of which is defined by a first cam profile, and the valve-opening rocker 12 is itself carried by a pivot on a supporting rocker 14 which is moved by a second cam profile.

In the valve train of FIG. 1A, two cams mounted on the same or different camshafts have cam followers 16 and 18 which transmit the movement of the two cams to the rockers 12 and 14 by way of push rods 20 and 22, respectively. In the valve train of FIG. 1B, the cams are mounted on a common assembled camshaft 30. A roller follower 32 transmits the motion of one cam to the rocker 14 which is pivoted about a fixed shaft 34 and carries the pivot shaft 36 of the valve opening rockers 12, each of the latter having a roller follower 38 in contact with a respective cam of the assembled camshaft 30.

FIG. 2 shows the way in which the two cam profiles 40 and 42 are added together in order to produce the valve lift 44. For some of the time when the valve is closed, neither cam profile is at its maximum lift, and this results in clearance being present in the valve train. An additional control spring is normally integrated into the system in order to dictate whether this clearance will occur between the valve tip and its rocker or between one of the cam followers and its associated cam lobe (see GB Patent Appln. No. 0426352.1 and U.S. Ser. No. 11/284,725).

By varying the phase of the cams acting on the two rockers relative to one another, it is possible to vary the overlap period and hence the event duration. The phase of the valve event can be varied by altering the phase of both cams relative to the crankshaft.

The rocker system is not stationary during the clearance phase of the motion, but moves from its valve closing position back to its valve opening position. The proposed designs utilise the clearance in the system and the movement of the rocker system in the clearance phase to effect the valve deactivation.

A number of different locations can be selected for integrating a valve deactivation systems into the summation valve trains shown in FIGS. 1A and 1B. In essence it is only necessary to interrupt either one of the paths transmitting motion, be it directly or indirectly, from one of the cams to the valve, to cause the valve to remain closed at all times. In the case of the OHC design shown in FIG. 1B, where a pair of valves is being actuated, the valve deactivation could be applied to one valve or to both valves as required.

In the first embodiment of the invention, shown in FIGS. 3A, 3B and 3C, valve deactivation is effected by preventing transmission of force at the interface between the valve stem and the valve-opening rocker 12.

The rocker design shown in FIG. 3 is intended as a direct replacement for the valve opening rockers 12 for either of the valve trains shown in FIGS. 1A and 1B.

The deactivation system is integrated into a clearance adjuster 50, which is mounted in the end of the rocker 12 and acts on the valve tip. The adjuster 50 comprises a hollow plunger 52 that can slide into the end of the rocker 12 and is biased into contact with the valve stem (not shown in FIG. 3) by means of a spring 54. The opposite end of the spring 54 acts on a ball 56 that can itself slide within an inner sleeve 55 located inside the plunger 52. The ball 56 which can itself be urged out of the inner sleeve 55 by application of hydraulic pressure serves as part of a latching system which prevents the plunger 52 from being retracted into the end of the rocker 12.

FIG. 3 shows the system in its locked position where the rocker will lift the valve. The lift is transmitted to the valve via the plunger 52, which is prevented from sliding into its bore in the rocker by the ring of balls 58 connecting it to an inner sleeve 55 which is in turn located by the clearance adjusting screw 60. The balls 58 are prevented from sliding inwards by the large central ball 56, which is held against an end stop by a spring and the contact forces of the smaller balls.

The valve is deactivated by applying oil pressure to a drilling in the rocker, which acts to force the central ball downwards against the action of the spring 54. The central ball 56 can only move when there is clearance between the rocker and the valve tip because it has to force the small balls away from the centre in order to pass through. The movement of the small balls pushes the plunger out of the rocker slightly due to the angle of the face on which they locate and this can only happen when the plunger is unloaded. The spring 54 also acts to move the plunger axially to a position where the small balls 58 can move freely.

When the rocker next contacts the valve, the plunger 52 will push the small balls inwards and retract freely into the rocker 12. If the oil pressure is removed, the large ball will move back against its stop under the action of the spring 54 the next time the system is in clearance. The contact of the small balls 58 on the larger ball 56 ensures that there are only two stable equilibrium positions, with the large ball being held against its upper stop, or against its retaining clip.

The latching system is an over-centre arrangement which cannot operate when the rocker is in contact with the valve tip, hence the switch between valve lifting and valve deactivation modes can only occur during the clearance part of the valve train cycle.

The system is also of a bi-stable design in that if the rocker is brought into contact with the valve whilst the system is in the process of switching, the contact forces the system into one or other of its stable positions. This avoids any extremely high forces being applied to the components of the latch.

This design can be applied to one or both valves of a pair, depending on whether single valve deactivation or cylinder deactivation are required. It would also be possible to switch a pair of valves independently if two separate switched oil feeds were provided—one for each rocker. Although it has been drawn for an OHC application, this design could be simply applied to a pushrod valve train system to achieve valve deactivation. In all cases a control spring is still required to maintain contact between both cam profiles and their respective followers.

An alternative design for the mechanism of FIG. 3 is shown in FIG. 4 in which the large central ball 56 is replaced by a sliding sleeve 66 that holds a ring of balls 58′ in engagement with the sliding plunger 52′ to lock it into position. The sleeve 66 is moved upwards as viewed hydraulically to release the latch and it moved into the illustrated latching position by a spring 64. The surface of the sleeve 66 that contacts the balls 58′ is profiled in order to give the system a bi-stable characteristic as described above. In other respects, the device will operate in a similar manner to the design in FIG. 3.

The embodiment of FIGS. 5 and 6 is similar to the embodiments of FIGS. 3 and 4 in that it provides a method for disconnecting the valve tip from the valve-opening rocker such that the opening rocker motion is no longer transmitted to the valve. However the deactivation system is operated mechanically, rather than by an oil pressure signal.

A first method for achieving this objective is shown in FIGS. 5A and 5B where control shafts 70 may be rotated in order to determine which valves are deactivated at any particular time. When a lever 72 on a rocker 12 is moved towards the valve by rotating the control shaft 70, the valve is deactivated. Having different profiled sections on the control shaft to act on each rocker will allow different combinations of valves to be deactivated.

FIG. 6 illustrates how the valve deactivation system operates in more detail. A ball-ended clearance adjuster 74 is threaded into a sliding cylinder 76 that has an interrupted external key 78 on both sides and runs in a corresponding slot in the rocker body. In the locked position (as drawn in FIGS. 6A and 6B), a latching plate 82 is located between the lower part of the key 78 on the sliding cylinder 76 and the underside of the body of the rocker 12, preventing the sliding cylinder 76 from moving and hence lifting the valve.

When the latching lever 72 is moved towards the valve, springs 80 between itself and the latching plate 82 become loaded, and the latching plate 82 will rotate on its pivot as soon as the system is in the clearance portion of the motion. As the system moves back towards the beginning of the valve lift, the lower section of the key 78 on the sliding cylinder 76 moves past the latching plate 82 and simply slides up into the rocker 12 rather than lifting the valve. A further spring 84 acts on the top of the sliding cylinder in order to maintain contact with the valve tip.

If the lever 72 is moved just as valve lift is about to commence, the latch plate 82 may not move quickly enough the avoid contact with the key on the sliding cylinder. In this case, the latch plate 82 will be forced back to its seated position in contact with the underside of the rocker body against the action of the two springs, and no damage to the moving parts will occur.

There will clearly be some movement of the latching lever 72 relative to the control shaft 70 during the operating cycle of the rocker, but this does not cause a problem as it is the position of the lever in the valve seated position that determines whether or not the valve will be deactivated.

An alternative mechanical valve deactivating system is shown in FIGS. 7 and 8. As with the previous design, the valve can be deactivated by allowing a sliding plunger 94 to move into the rocker instead of transmitting the rocker motion to the valve.

Each rocker is fitted with a lever 96, the position of which determines whether the valve lift will be deactivated. Positioning of the lever 96 close to the pivot point of the rocker 12 minimises its movement relative to the static parts of the cylinder head and a number of fairly simple methods for moving the levers are feasible. One such method is shown in, and will be described below by reference to, FIG. 10.

The different views in FIG. 8 show the design of the valve-lifting rocker in more detail. The valve lift is enabled and deactivated via a sliding plate 98 that pivots about a pin 92 mounted in the rocker body. The plate 98 slides against the underside of the rocker body, and has a bore 100 through which the ball-ended plunger 94 for lifting the valve is able to pass. When the bore 100 in the plate 98 is aligned with the plunger bore in the rocker, the plunger is free to slide and the valve will be deactivated. Rotating the plate through a small angle about the pin 92 allows it to engage in a recess 102 machined into the plunger 94, and this will lock the plunger 94 in position to transmit the rocker motion to the valve.

An interlock system is provided to ensure that any change from valve activation to valve de-activation may only occur during the clearance phase of the rocker motion. This is achieved by a pin 104 that is fitted to the plunger 94 and passes through a slot 106 in the rocker body, into a profiled slot 108 in the sliding plate 98.

The plunger 94 is loaded by a spring 110, so that as clearance appears in the rocker system, the plunger will move out of its bore and the pin 104 will move to the bottom of the ‘V’ profile of the slot 108, rotating the plate to a ‘central’ position between the locked and unlocked positions. As the system approaches the point of valve lift, the clearance reduces and the pin travels up one or other side of the ‘V’, moving the plate into one of its extreme positions.

The movement of the plate 98 is determined by a torque spring 112 that acts on the pivot pin 92 of the plate 98 and reacts against the control lever 96. Moving the control lever therefore determines the direction in which the plate is preloaded by the torque spring 112, and this in turn determines whether the interlock pin 104 will move up the short or the long side of the ‘V’ slot.

FIGS. 9A to 9F show the operation of the interlock system as the system moves from the valve lift position (FIG. 9A) through the clearance position (FIG. 9C) and into the valve-deactivated position (FIGS. 9E). The corresponding views of the underside of the rocker as seen in FIGS. 9B, 9D and 9F, respectively, show how the plate engages with the plunger to transmit the rocker motion to the valve.

A similar deactivation system can be applied to an engine using bridge pieces to transmit the lift of a single rocker to a pair of valves. The bridge piece design is particularly popular for engines using ‘twisted’ or ‘diamond pattern’ valve arrangements (as shown in FIG. 10) where different rocker geometry would be necessary to actuate the valves of each pair individually.

FIGS. 10 to 12 show how the deactivation method described by reference to FIGS. 7 to 9 can be used to switch from two-valve operation via a bridge piece to single valve operation. This is achieved by deactivating a plunger 124 that acts on the centre of the bridge 130 and actuating a single valve via an insert 132 that passes through the bridge piece 130 (see FIG. 12). The valve lift of the single valve will be less than that of the pair of valves because it is closer to the pivot point of the rocker 12 than the centre of the bridge 130.

FIG. 10 also shows how the control levers 96 on the rockers may be actuated by a simple plate 140 mounted to the cylinder head cover that is free to slide parallel to the camshaft axis. The plate 140 engages the control levers 96 of the rockers via slots, such that changing the position of the plate 140 will cause all of the levers 96 to rotate. The plate is engaged with an eccentric 142 at one end such that rotating the eccentric will cause the plate 140 to move.

The design of the valve-lifting rocker may be described more easily with reference to the different views of FIG. 11. The rocker 12 is fitted with two spherical pads 150, 152. The first pad 150 acts on the centre of the bridge piece 130, whilst the second pad 152 acts on the separate insert 132 in the bridge piece 130 that opens a single valve 10B. The first pad 150 is part of the sliding plunger 124 that may be disconnected from the rocker 12 by the valve deactivation system, whilst the second pad 152 is fixed and may be threaded into the rocker 12 for adjustment purposes.

FIG. 11 shows the design of the deactivation system for the plunger 124 that acts on the centre of the bridge piece 130. A moving plate 160 engages with a step on the plunger 124 in order to prevent it from sliding in the rocker, and the plate 160 is provided with an interlock arrangement to ensure that it may only be in one of its two end positions at the point of valve lift. In principle this system operates in an identical manner to that described by reference to FIGS. 7 to 9.

FIG. 12 shows the arrangement of the bridge piece 130 and the insert 132, which allows a single valve 10B to be operated through the bridge. Any of the previously described embodiments may be adapted to work with a bridge piece of this type as outlined above.

All the embodiments described above have operated on the principle of decoupling the valve actuating rocker from the valve stem, that it is say allowing the rocker to oscillate without transmitting its movement to the valve. There are however other ways of integrating a valve deactivation system into a summation valve train such as by decoupling the rockers from one another, decoupling the rockers from the cams or push rods or by forming one of the rocker of two parts that can be selectively locked to one another.

The embodiment of FIGS. 13 and 14 deactivates the valve lift by isolating a pivot 200 of the valve-lifting rocker 12 from the movement of the supporting rocker 14.

FIGS. 13 and 14 illustrate how this may be achieved on an OHV engine by mounting the valve-opening rocker 12 on a separate eccentric sleeve 200. The eccentric sleeve 200 is mounted for rotation about a fixed pivot shaft 202, which also supports the second ‘supporting’ rocker 14. A latching system 210 is integrated with the eccentric 200 in order to connect the eccentric for rotation with the second rocker 14 and removing this connection acts to deactivate the valve lift.

The latching system 210 is designed to transmit rotation in only one direction. This is achieved by forming an end surface 214 of a latch pin 212 (see FIGS. 14B and 14C) with a ramp which terminates in an abrupt step, thereby acting in a manner analogous to a pawl and ratchet. During the valve lift the latch pin is forced against the driving step on the second rocker (see FIG. 14A) causing the eccentric to rotate with the rocker. During the clearance portion of the valve train cycle whilst the valve is closed, the second rocker is still in motion and this causes the latch pin to move away from the driving step on the closing rocker. The contact face 214 of the latch pin 212 and the second rocker 14 are profiled such that the relative motion forces the latch pin into its bore in the eccentric against the action of a spring 216. As the system approaches the valve opening position, the latch pin 212 moves back into its engaged position under the action of the spring 216.

Valve deactivation is achieved by holding the latch pin 212 in its disengaged position so that it is unable to re-engage under the action of the spring 216. Two different methods for doing this are illustrated in FIGS. 14B and 14C which show the design of the eccentric 200. FIG. 14B illustrates a locking ball 220 that will prevent the latch pin from returning when it is supplied with oil pressure whilst FIG. 14C shows a mechanical system 230, shown as being a ball catch, that will always trap the pin 212 in its withdrawn position unless an external force is applied to the end of the pin to re-engage it. This could be achieved with a spring-loaded mechanical system.

A similar arrangement is possible for the OHC design where the supporting rocker 314 may be divided into a number of sections (314a, 314b and 314c) as shown in FIGS. 15A and 15B. In this way either one or both of the valves may be deactivated by disconnecting the respective linkages 314a, 314c from the central section of the support rocker 314b.

A number of possibilities exist for locking the outer linkages such that they rotate with the centre section of the location rocker, including a latch pin design as described above. Alternatively a different connection system may be used as will be described below by reference to FIGS. 16 and 17.

As shown in the exploded view of FIG. 16C locking may be achieved via a stepped pin 312. The step of the pin 312 engages with a corresponding step on the central section 314b of the support rocker 314 during the valve lift, and the two parts move out of contact during the clearance portion of the motion. The stepped pin 312 can be pushed into a disengaged position by supplying oil pressure to a small hydraulic piston located in a bore in the central section 314b of the rocker.

The locking arrangement can be seen more clearly in FIG. 17, where FIG. 17C shows the oil drilling 316 used to deactivate the lift and FIGS. 17A & 17B and FIGS. 17D and 17E show the different positions of the locking pins 312. FIGS. 17A and 17B show the system in its disengaged position whilst the FIGS. 17C and 17D show the system in its engaged position where the two pistons 318 are pushed fully into the central section 314b of the rocker and the locking pins 312 are engaged with the drive step on the central section 314b of the rocker.

The stepped locking pins 312 need to be retained in a suitable angular alignment in order to engage properly, so each is provided with a slot 320 into which is engaged a ball 322 to limit the angular rotation of the pin 312 (see FIG. 16C). A spring 324 behind the pin is designed to act as combined compression and torque spring so that it acts to urge the locking pin 312 out of its bore and to hold it against the end of its angular rotation range.

It can be seen from FIG. 17B that the disengaged pin 312 is designed to move into a position where its flat contact surface is not aligned with that of the centre section 314 of the rocker. This ensures that the pin 312 can only engage when there is some clearance in the system and this prevents the pin starting to engage right at the point of valve lift commencing and causing damage to the parts of the system. Once engaged, the pin will automatically be rotated to the correct position against the action of its spring as the clearance in the system reduces.

The embodiment of FIG. 18 deactivates the valve by disconnecting the motion of the cam follower from the rocker system and offers the opportunity for integrating the deactivation system with a control spring for positioning the rocker system during the clearance phase of the cycle.

FIG. 18 shows the design for an OHC application, where the valve-operating rocker 412 has been divided in to two sections 412a and 412b that are connected by a pivot shaft 414. The cam follower 416 is mounted into the lower section 412b of the rocker and is able to move relative to the main section 412a of the rocker against the action of a control spring 418 that is installed in the main section 412a of the rocker. During the clearance portion of the motion cycle, the cam follower 416 will be held in contact with the cam and the clearance adjuster 420 will be held in contact with the valve by the control spring 418. As the system moves back towards the start of the valve lift cycle, a latch pin 422 may be engaged to transmit the motion of the lower section 412b to the main section 412a of the rocker in order to lift the valve. If the pin 422 is held out of contact with an abutment 424 on the main section of the rocker, the section 412b will continue to move independently of the main section 412a of the rocker, thereby deactivating the valve lift.

FIGS. 19A to 19C illustrate how a simple spring may be integrated with the rocker assembly to hold the pin 422 out of engagement with the abutment 424. Valve lift is activated by forcing the pin 422 downwards into the path of the abutment 424 via a strip of spring steel 450 installed into the engine cover. The position of the steel strip 450 is determined by its contact with a control shaft 452 mounted in the cover. The control shaft 452 has a number of profiled sections that each contact the steel strips 450 associated with the different rockers. When the steel strip is contacted by the high portion of the profile, the latch pin 422 is forced to engage and valve lift is produced, but when the steel strip 450 contacts the low portion of the profile, the latch pin 422 will disengage and the valve will be deactivated.

The operation of the valves is controlled by the rotation of the control shaft 452, but it is not necessary for all of the valves to be deactivated at the same time. By producing the control shaft 452, as shown in FIG. 20, with a number of different profiles, it is possible to provide a variety of different control shaft positions that will deactivate different combinations of valves.

The principle of integrating a control spring with the valve deactivation system can also be applied to an OHV system by integrating the control spring and the deactivation system into the cam follower assembly. FIG. 21A to 21E shows how this may be achieved using an over-centre locking system similar to that previously described by reference FIG. 3.

FIG. 21B shows the cam follower 16 in its fully extended position with the large central ball 510 in its upper position to force a ring of smaller balls 512 outwards into a recess in the main body of the cam follower. A hole is provided on the left side of the follower to feed the deactivation oil supply into this recess and force the central ball 510 into its lower position. A second oil drilling is provided on the right hand side to allow lubricating oil into the cam follower.

FIGS. 21C to 21E show the arrangement of the balls in the three different positions of the follower. FIG. 21C shows the follower fully extended in order to control the rocker system, FIG. 21D shows the follower in its locked position where the ring of locking balls 512 are engaged with the lower face of the cut-out in the follower bore, and the FIG. 21E shows the follower in its fully compressed state (valve deactivated) where the central ball 510 has been moved into its lower position by oil pressure and the ring of smaller balls 512 have moved inwards in order to pass the edge of the recess.

An alternative design for integrating a deactivation system into a cam follower is shown in FIG. 22. The valve deactivation in this case is achieved via a pair of splined components 610, 612 that may either be aligned so that the inner spline will slide into the outer spline, deactivating the valve lift, or misaligned so that the end of the inner spline will contact the top face of the outer spline, transmitting the cam lift to the rocker system.

The internally splined component 612 has a helical groove 614 machined into its outer diameter, which is engaged by a ball 616 that is permanently fitted to the body of the cam follower. Oil can be supplied to the cavity below the internally splined component in order to move it to a higher position and this also causes it to rotate because of the helical groove 614. When the lower splined component 612 is held in this upper position, the upper spline can pass through it without making contact. When the lower splined component 612 is in its lower position, the two sets of splines are misaligned and so the upper spline cannot enter the lower spline.

The lower splined component 612 can only move to its upper position when the valve train is in the clearance portion of the cycle and the cam follower is fully extended. If it should be in the process of movement when it comes into contact with the upper spline, it will simply be forced back into its bore and take up the locked position.

A pair of slots in the bore of the follower locates the upper spline 610 and allows it a small range of angular travel. It is preloaded against one side of these slots by a torque spring 618 that is located beneath it in a housing 620, which also engages into the slots in the follower bore. This allows the upper splined component 610 to rotate with the lower spline when the pair are engaged and the lower spline is forced back into its bore under the action of the cam lift.

Claims

1. An internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including

two rotatable cams,

a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and

a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams, wherein

an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem,

a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and

the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.

2. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and both valves are adapted to be deactivated simultaneously.

3. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and only one valve of the pair is capable of being deactivated.

4. An internal combustion engine as claimed in claim 1, wherein the rocker system actuates a pair of valves, and each valve of the pair may be selectively deactivated.

5. An internal combustion engine as claimed in claim 3, wherein the rocker system actuates a pair of valves, and deactivation one valve of the pair alters the lift characteristic of the second valve.

6. An internal combustion engine as claimed in claim 1, wherein a plunger is mounted in a rocker in such a manner as to permit the plunger to be retracted into the rocker in order to deactivate the associated valve and the latching mechanism serves to inhibit retraction of the lash adjuster so as to cause the valve to be actuated by movement of the rocker.

7. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is hydraulically operated.

8. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is mechanically operated.

9. An internal combustion engine as claimed in claim 6, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.

10. An internal combustion engine as claimed in claim 6, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.

11. An internal combustion engine as claimed in claim 1, wherein one of the rockers is formed of two sections that are pivotable relative to one another, one section being cam actuated and the other serving directly or indirectly to actuate a valve, pivoting of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve.

12. An internal combustion engine as claimed in claim 11, wherein a control spring acts between the two sections of the rocker to ensure that the respective sections maintain a contact force on the cam lobe and the valve tip throughout the operating cycle of the rocker system.

13. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is hydraulically operated.

14. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is mechanically operated.

15. An internal combustion engine as claimed in claim 11, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.

16. An internal combustion engine as claimed in claim 11, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.

17. An internal combustion engine as claimed in claim 1, wherein a cam follower is formed in two sections that are slidable relative to one another, one section being cam actuated and the other serving to actuate one of the rockers, sliding of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve.

18. An internal combustion engine as claimed in claim 17, wherein a control spring acts between the two sections of the cam follower to ensure that the respective sections maintain a contact force on the cam lobe and the corresponding rocker throughout the operating cycle of the rocker system.

19. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is hydraulically operated.

20. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is mechanically operated.

21. An internal combustion engine as claimed in claim 17, wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position.

22. An internal combustion engine as claimed in claim 17, wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.